Apparatuses of the above type are used for substance separation or substance synthesis processes in which, for example, two process spaces are separated from one another by a partially permeable large-area layer, for example in the form of a membrane. For example, in the case of synthesis processes of a PEM fuel cell, the process spaces are separated from one another by selectively permeable layers, in particular membranes. The layers or membranes are in this case predominantly permeable to ions which are used for charge transfer.
In a cell stack of an apparatus of this type, passages for routing process substances penetrate through the selectively permeable layers in the interior of the cell stack. The layers are sealed at their outer edge and at their edges adjoining the passages.
A certain minimum surface area of membrane or layers has to be made available for the desired chemical or electrochemical separation or synthesis process. The consumption of surface area and therefore of layer material is increased by the fact that the passages and their seals are routed through the layers. However, the material required to produce the layer, in particular in the case of PEM fuel cells, is relatively expensive. Therefore, it is fundamentally the aim for only small amounts of such material to be installed in the apparatus.
Apparatuses with high process flows require relatively large passage cross sections within the layers, and consequently the desired cost objectives cannot be achieved, on account of the large amount of material cut from the layers.
In addition to efficient utilization of the material of the layers, it is also a requirement for the individual process substance to be distributed uniformly over the area of the layers in the cell stack. Furthermore, the overall pressure loss in the passages for feeding and discharging the individual process substance should be as low as possible.
U.S. Pat. No. 5,484,666 A has disclosed a cell stack of an electrochemical cell in which feed and discharge passages are routed through a multiplicity of membranes. This keeps the total volume of the cell stack relatively small, but the amount of material cut from the membranes for the passages is large. Furthermore, tie rods for connecting and clamping the cell stack are formed through the passages in the cell stack. The tie rods are supported on front and end plates of the cell stack, in which connections for the passages are also formed.
U.S. Pat. No. 5,543,240 A has disclosed an overall fuel cell stack in which a process substance is routed to individual cell stacks through external supply passages. The external supply requires additional components, and in particular valves for connection to the cell stacks, and makes it more difficult to achieve a space-saving and inexpensive design of the overall fuel cell stack.